Are there any cards in the game which are almost always better to play the normal version or almost always better to play the elite version? Or are they usually well balanced?

Most of the time you'll want to use Elites. Everybody has their own list of exceptions. Mine are regular HKs and Alliance Rangers.

Are there any cards in the game which are almost always better to play the normal version or almost always better to play the elite version? Or are they usually well balanced?

Generally, only one or the other is worth playing, and it usually depends on the role they play and the point cost involved. For objective Grabbers and expensive units you generally want the regular. Examples include Hired Guns, Imperial Officer, and Alliance Smuggler for cheap objective/support, and HKs, Trandos, Wookiees, and Royal Guards are generally only played as Regulars because of the Elites high cost.

On the other hand, for most attacker units of less than 10 points, you want the Elites over the regulars: Echo Base Troopers, Rebel Troopers, Rebel Saboteurs, Gamorrean, Weequay, Wing Guard, Heavy Stormtrooper, Stormtrooper, ESnowtroopers, and Probe Droids all come to mind right away.

There's plenty.

Here are the units that you'll almost NEVER see played.

Elite Wookies

Elite Hired Guns

Regular Gamorrean Guard

These ones are very rare to see or usually require a specific list

Elite Royal Guard

Elite Ugnaughts

Both Wampas

Both E-Web Engineers

Elite Imperial Officers (usually only paired with a big hitter like Vader or AT-ST)

Regular Probe Droid (usually as filler or in a Sorin list)

Regular Jet Trooper (usually as filler or in a Sorin list)

These you'll see from time to time but are generally considered over priced or just not good.

Both Trandoshans

Elite HKs

Regular Wookies
Elite Rebel Troopers (replaced by Rangers)
Both Wing Guard (too many better Merc units to compete with)

Regular cards that are common to see
Alliance Rangers

Royal Guard

HKs

Hired Guns

Nexu

Ugnaught

Officers

All other regular cards are either in the "rarely seen" or the "never played" list

All other elite cards that I haven't already mentioned are regularly used

I agree with Inquisitorz except for regular ugnaughts are not very common. If you are running Ugnaughts you usually go all in and run both regulars and elites. They have a unique deployment cost that might tempt you to use them for filler, but they are not worth running by themselves.

I disagree, an urgnaut by itself can contest two terminals because the junk droid contests control for them. then your opponents have to waste an attack on the junk droid or not get their command card.